A reaction of a phenol compound and formaldehyde in the presence of an acidic catalyst has been known as a reaction for producing a phenol-novolak resin or the like. It has been also disclosed that an aldehyde compound, such as acetaldehyde, propionaldehyde, isobutyl aldehyde, crotonaldehyde and benzaldehyde, is reacted to produce a polyphenol compound (Patent Document 1) and a novolak resin (Patent Document 2).
It has been also disclosed that a hydroxybenzaldehyde or the like, which has both functions of phenol and aldehyde, is reacted to produce a novolak type resin (Patent Document 3).
The polyphenol compounds and the novolak resins are used as a coating material and a resist resin for a semiconductor, and is demanded to have heat resistance as one of the capabilities of these purposes. It has been ordinarily known that the heat resistance is enhanced by increasing the carbon concentration in the resin or decreasing the oxygen concentration therein. A method of increasing the carbon concentration and decreasing the oxygen concentration includes a method of introducing an aromatic hydrocarbon component. Under the circumstances, a polymer having the structure represented by the following formula (i.e., a acenaphthene resin) has been known (Patent Document 4).
wherein R1 represents a monovalent atom or a group; n represents an integer of from 0 to 4; and R2 to R5 each independently represent a hydroxyl group or a monovalent atom or group.
However, the material has problems that it is expensive, severe reaction conditions are required for producing the resin, many reaction steps are required to make the reaction complicated, and the like.
Microfabrication by lithography using a photoresist composition is performed in production of semiconductor devices, and associated with the increase of integration degree and increase of speed of an LSI in recent years, further miniaturization through pattern rules is demanded, but the lithography using light exposure used as a recently general-purpose technique is now approaching the essential limitation in resolution derived from the wavelength of light source.
The light source for lithography used upon forming a resist pattern has a decreasing wavelength from a KrF excimer laser (248 nm) to an ArF excimer laser (193 nm). Associated with the miniaturization of the resist pattern, however, the problems of resolution and collapse of the resist pattern after development occur, which derive a demand of thinning of the resist. Accordingly, it is difficult to assure the thickness of the resist pattern that is sufficient for processing the substrate, and thus such a process may be required that the function of mask is imparted not only to the resist pattern, but also to a resist underlayer film formed between the resist and the substrate to be processed. As the resist underlayer film for the process, currently, such resist underlayer films are being demanded as a resist underlayer film for lithography that has a selective ratio of dry etching rate close to the resist, a resist underlayer film for lithography that has a selective ratio of dry etching rate smaller than the resist, and a resist underlayer film for lithography that has a selective ratio of dry etching rate smaller than the semiconductor substrate, which are different from the ordinary resist underlayer film having a large dry etching rate. These resist underlayer films may also be imparted with an antireflection function, and thus may also have a function of an ordinary antireflection film (see, for example, Patent Documents 5, 6 and 7).
The present inventors have proposed, as a material that is imparted with an antireflection function to an ArF excimer laser and has high etching resistance, a composition for forming an underlayer film containing a naphthalene formaldehyde polymer (see Patent Document 8). For conducting further miniaturization of the resist pattern, however, there is a demand of further enhancing the etching resistance.
A two-layer resist method has also been proposed, which is superior to the three-layer resist method owing to the less number of process steps. In the two-layer resist method, after forming an underlayer film on a substrate in the similar manner as in the three-layer resist method, a photoresist film containing a silicon-containing polymer is formed as an upper layer thereof, a resist pattern is formed by an ordinary photolithography technique, and etching with oxygen plasma is performed with the resist pattern as a mask, thereby transferring the resist pattern to the underlayer film. Etching with a carbon fluoride gas or the like is then performed with the resist pattern as a mask, thereby forming the pattern on the substrate (Non-patent Document 1).